I will sketchily illustrate how the theory of symmetry helps in determining
solutions of (deterministic) differential equations, both ODEs and PDEs,
staying within the classical theory. I will then present a quick discussion of
some more and less recent attempts to extend this theory to the study of
stochastic differential equations, and briefly mention some perspective in this
direction.Comment: Review paper (119 pages) here in bookstyle. The published version may
differ from the present (preprint) one. Version 2 (November 2017): due to a
mistake in a basic formula (in a previous paper of mine) the content of
Section 5.5 gives wrong statement; an ERRATUM has been added at the end of
the file; see also arXiv:1711.01999 for correct results on that topi